For additional meanings of "Knot", please see Knot.
Knot was a unit of velocity equal to one nautical mile per hour.
During USS Voyager's visit to what was later determined to be the Sky Spirits' homeworld in 2372, they experienced odd weather changes. While on the planet they experienced surface conditions with the equivalence of gale force winds, but after they left, conditions returned to normal, with winds at a mere 2 knots. (VOY: "Tattoo")